Respiratory Substrates and Quotient

• Respiratory substrate: Organic molecule used for respiration to release energy and make ATP (e.g. glucose), all food molecules are converted to those that enter cellular respiration pathway; some at glycolysis, others at Krebs cycle
• All catabolic pathways for carbohydrates, proteins, and lipids connect; metabolic pathways are porous; substances enter from and leave for other pathways (not closed system; many products in pathways are reactants in others too)
• Oxidative phosphorylation produces most ATP, protons flow through ATP synthase; substrate with more hydrogen atoms per mole: more protons flow and increase ATP production; requires more oxygen per mole of substrate for respiration